This application claims the priority of Korean Patent Application No. 2003-74662, filed on Oct. 24, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical scanner having an MEMS (micro electromechanical system) structure in which a frequency is tunable, and more particularly, to an optical scanner in which a resonant frequency is tunable by using a tuning electrode.
2. Description of the Related Art
Microactuators are used as scanners to deflect a laser beam in projection TVs. U.S. Patent Publication Application No. 2003-39089 discloses an example of an MEMS type scanner.
In an optical scanner disclosed in U.S. Patent Publication Application No. 2003-39089, a stage seesaws with respect to a torsion spring supporting the stage as a center shaft. As the stage is seesawing, light incident on a flat reflection mirror formed on the stage is scanned. The optical scanner deflects the stage connected to a driving electrode by applying an electrostatic force between a driving comb electrode and a fixed comb electrode.
In the MEMS type scanner, when the stage is driven in a resonant frequency range, a driving angle of the stage increases and a driving voltage is lowered. However, when an MEMS structure is accurately manufactured, it is very difficult to manufacture an actuator having a predetermined natural frequency due to a deviation in process. Also, a change in the resonant frequency may occur according to a change of surrounding environment.
U.S. Pat. No. 6,535,325 discloses a method of controlling a resonant frequency of an MEMS type optical scanner. That is, after a plurality of tuning tabs are installed at an edge portion of a stage, the tab is removed by a laser trimming or mechanical force while a frequency is measured, so that the weight of a mirror body is reduced. Thus, by increasing the frequency, the optical scanner is driven at a resonant frequency.